1. Field of the Invention
The present invention relates to the transversal filter art, and more particularly to a logic controlled transversal filter using charge transfer structures such as charge-coupled-devices or bucket brigade devices.
2. Description of the Prior Art
The use of charge transfer devices for transversal filtering has been taught in the prior art, for example, in the publication "Transversal Filtering Using Charge-Transfer Devices" by Dennis D. Buss, Dean R. Collins, Walter H. Bailey, and C. Richard Reeves, IEEE J. Solid-State Circuits, Vol. SC-8, No. 2 April 1973, pp 138-146. This publication presents techniques for making transversal filters using charge-coupled devices and bucket-brigade devices. In the charge-coupled device transversal filter, the delayed signals are sampled by measuring the current flowing in the clock lines during transfer, and the sampled signals are weighted by a split electrode technique. In the bucket brigade transversal filter, the delayed signals are "tapped" with a source follower whose load determines the weighting coefficient.
The transversal filters described in the cited publication require precise tap weights over a wide range of values which is difficult to achieve using the split electrode described or other known techniques. The transversal filter of the present invention requires only weighting of +1, -1 and 0 and additionally can be programmed, that is, logic controlled.
Another example of an analog filter using charge transfer techniques is U.S. Pat. No. 3,819,958 issued June 25, 1974 to Gosney on an application filed Nov. 3, 1972 and assigned to Texas Instruments, Incorporated. The filter described in the cited patent also requires completed weighting, incorporates the split electrode technique, and is not logic controlled.
In addition, there are copending patent applications assigned to the present assignee which describe certain specific devices and techniques which are incorporated in the present invention. U.S. application Ser. No. 625,425 describes a charge packet replicator, U.S. patent applications Ser. Nos. 662,626 and 670,781 describe charge packet generators, and U.S. patent application Ser. No. 636,862 describes a circuit for injecting charge packets into an input circuit.